Method and apparatus for transmitting and receiving MCS index for 256QAM in wireless access system

1. A method for decoding data in a wireless access system, the method performed by a user equipment (UE) and comprising:

receiving a higher layer signal including an indication that 256 quadrature amplitude modulation (256QAM) is to be enabled;

receiving, via a physical downlink control channel (PDCCH), downlink control information (DCI) including an index field representing a modulation and coding scheme (MCS);

receiving data via a physical downlink shared channel (PDSCH) scheduled by the PDCCH; and

decoding the received data using the MCS represented by the index field,

wherein the UE has a first MCS index table supporting up to 64 quadrature amplitude modulation (64QAM) and a second MCS index table supporting up to the 256QAM, and

wherein the received data is decoded based on the first MCS index table even though the second MCS index table has been enabled to the UE, when the DCI has been scrambled with a semi persistent scheduling radio network temporary identifier (SPS-RNTI).

2. The method according to claim 1 , further comprising:

determining a modulation order and a transport block size (TBS) index depending upon an MCS index in the first MCS index table.

3. The method according to claim 1 , wherein the UE decodes the received data using a modulation scheme indicated by the index field at the first MCS index table.

4. The method according to claim 1 , wherein the first MCS index table and the second MCS index table are represented by 5 bits.

5. A user equipment (UE), comprising:

a receiver configured to:

receive a higher layer signal including an indication that 256 quadrature amplitude modulation (256QAM) is to be enabled,

receive, via a physical downlink control channel (PDCCH), downlink control information (DCI) including an index field representing a modulation and coding scheme (MCS), and

receive data via a physical downlink shared channel (PDSCH) scheduled by the PDCCH; and

a processor configured to decode the received data using the MCS represented by the index field,

wherein the UE has the first MCS index table supporting up to 64 quadrature amplitude modulation (64QAM) and a second MCS index table supporting up to 256QAM, and

wherein the received data is decoded by the processor based on the first MCS index table even though the second MCS index table has been enabled to the UE, when the DCI has been scrambled with a semi persistent scheduling radio network temporary identifier (SPS-RNTI).

6. The UE according to claim 5 , wherein the processor is further configured to determine a modulation order and a transport block size (TBS) index depending upon an MCS index in the first MCS index table.

7. The UE according to claim 5 , wherein the UE decodes the received data using a modulation scheme indicated by the index field at the first MCS index table.

8. The UE according to claim 5 , wherein the first MCS index table and the second MCS index table are represented by 5 bits.

9. A method for transmitting downlink data in a wireless access system, the method performed by an evolved Node B (eNB) and comprising:

transmitting a higher layer signal including an indication that 256 quadrature amplitude modulation (256QAM) is to be enabled;

transmitting, via a physical downlink control channel (PDCCH), downlink control information (DCI) including an index field representing a modulation and coding scheme (MCS); and

transmitting data via a physical downlink shared channel (PDSCH) scheduled by the PDCCH,

wherein the eNB has a first MCS index table supporting up to 64 quadrature amplitude modulation (64QAM) and a second MCS index table supporting up to the 256QAM, and

wherein the transmitted data is encoded based on the first MCS index table even though the second MCS index table has been enabled, when the DCI has been scrambled with a semi persistent scheduling radio network temporary identifier (SPS-RNTI).

10. The method according to claim 9 , wherein the data is decoded by a user equipment (UE) using the MCS represented by the index field, and

a modulation order and a transport block size (TBS) index is determined depending upon an MCS index in the first MCS index table.

11. The method according to claim 9 , wherein the first MCS index table and the second MCS index table are represented by 5 bits.

12. An evolved Node B (eNB), comprising:

a transmitter configured to:

transmit a higher layer signal including an indication that 256 quadrature amplitude modulation (256QAM) is to be enabled,

transmit, via a physical downlink control channel (PDCCH), downlink control information (DCI) including an index field representing a modulation and coding scheme (MCS), and

transmit data via a physical downlink shared channel (PDSCH) scheduled by the PDCCH; and

a processor configured to encode the data using the MCS represented by the index field,

wherein the eNB has the first MCS index table supporting up to 64 quadrature amplitude modulation (64QAM) and a second MCS index table supporting up to 256QAM, and

wherein the data is encoded by the processor based on the first MCS index table even though the second MCS index table has been enabled, when the DCI has been scrambled with a semi persistent scheduling radio network temporary identifier (SPS-RNTI).

13. The eNB according to claim 12 , wherein the data is decoded by a user equipment (UE) using the MCS represented by the index field, and

a modulation order and a transport block size (TBS) index is determined depending upon an MCS index in the first MCS index table.

14. The eNB according to claim 12 , wherein the first MCS index table and the second MCS index table are represented by 5 bits.